Its in that same section E of Lasor's.
The difference maybe a notified difference to JAR for the Spanish.
Every country can opt out of certain bits they just have to publish a difference.
I am not suprised no one at the belgrano wants to put there kneck on the line with your case. The easy option for them is going to be to say no.
I suspect that as they use the IR as the only check where a CAA staff examiner gets their hands on you for a check and the CAA gets the money directly. They won't be in the mind set to give you any slack when it comes to you gaining a rating on a British license through a Spanish FTO and Spanish examiner.
This mix and matching of Licenses and ratings under JAR is great in theory but in practise it is very rare that it actually works smoothly, and I suspect the 2-3000 pounds you will save by doing it in a Spanish FTO will not be a saving in the long run. Even in the type rating examiner world there are all sorts of problems with British TRE's signing other member states licenses and the associated paper work trail.